Build a webextension for firefox

I require an extension for firefox and chrome (same extension). We currently have an extension that can execute a command on the operation system (windows) when a link on our webpage is clicked. Since firefox is changing to webextension, we need to update this plugin to the new system. Extra points if we can do this directly, we will also accept if we need to install an exe that can redirect the call from the webextension to the OS (like our current NaCl chrome extension) What we want in the end: - WebExtension that can execute a command on a windows system triggered by a mouseclick (in JS). - The extension needs to remember what webpage it was send from and needs to white-list or ask for confirmation to white-list (ex by accessing/writing the registry) - Instructions/insights on how to distribute & install this extension with our customers - Working example - Documentation on the complete project What we can provide: - Old extension (chrome/firefox) - Installer for our chrome extension (written in innoscript) - Information and experience